This invention relates generally to steam turbines and, more specifically, to attaching steam turbine buckets to steam turbine wheels.
At least some known steam turbine buckets are subjected to high centrifugal loads. Specifically, buckets located in the last few stages of low pressure wheels may be more stressed than buckets in other stages due to centrifugal loads caused by rotation of steam turbine wheels. Such loads induce higher average and local stresses in the connective dovetails. Stress corrosion cracking (SCC) in the low pressure buckets is a serious concern and is driven largely by local stresses. As such, higher local stresses can lead to lower fatigue life of wheel and bucket dovetails. With an increasing demand for longer and longer buckets, the dovetails are required to operate under higher loads.
For at least some known low pressure turbines, the rotor wheel may be more limiting than the bucket. Specifically, the material used to manufacture at least some known buckets is more resistant to SCC than the material used for wheels. An effective means of avoiding SCC failure in low pressure wheels may be to reduce the local stresses in the wheel dovetail.